The invention relates to a process for the preparation of 1,4-butanediol by reaction of allyl alcohol with carbon monoxide and hydrogen in the presence of a soluble rhodium catalyst, a phosphine promoter and a solvent.
1,4-Butanediol is a valuable commercial product which finds application on a large scale, in particular as intermediate in the preparation of polyesters, polyurethanes, butyrolactone and tetrahydrofuran.
The commercial production of 1,4-butanediol relies virtually exclusively on the Reppe process, in which acetylene and formaldehyde are converted into 2-butyn-1,4-diol, which is hydrogenated to form 1,4-butanediol. In order to avoid the drawbacks involved in the use of acetylene in the Reppe process, a number of other pocesses have been proposed of which, according to Chemical Economy and Engineering Review, September 1980, 12 (No. 9), pp. 32-35, the one based on hydroformylation of allyl alcohol is the most attractive process for use on an industrial scale.
In this process--as described for instance in U.K. Patent Specification No. 1493154--allyl alcohol is first converted into hydroxybutyraldehyde by hydroformylation using a rhodiumcarbonyl complex as catalyst, an excess of a phosphine ligand and an organic solvent which is immiscible with water. Then the hydrobutyraldehyde formed is extracted from the organic solvent with water and subsequently hydrogenated to form 1,4-butanediol.
In the U.K. Patent Specification No. 1565719 a process is described in which allyl alcohol is converted direct into 1,4-butanediol in yields of up to 50%, by reacting the allyl alcohol with carbon monoxide and hydrogen in the presence of a rhodium catalyst and a tertiary phosphine containing at least one aliphatic hydrocarbyl group. In this process a solvent can advantageously be used which optionally may be immiscible with water and from which the 1,4-butanediol can be recovered by extraction with water.
It has now surprisingly been found that allyl alcohol can be converted direct into 1,4-butanediol in higher yields than mentioned in U.K. Patent Specification No. 1565719, when the reaction of allyl alcohol with carbon monoxide and hydrogen is carried out in the presence of a rhodium catalyst in combination with a trialkyl phosphine as ligand and certain carbonitriles--which will be defined hereinafter--as solvents.